This invention relates generally to control systems for glassware forming machines, and deals more particularly with a system which incorporates a general purpose digital computer for storing a sequence of events within a machine cycle, and the system is capable of controlling the operation of the machine without the necessity of generating, during each feeder cycle, multiple pulses from the glass feeder which provides gobs to the machine, or from a drive shaft such as that associated with the take away conveyor which carries the glassware articles away from the machine.
Prior art approaches to the electronic control of glassware forming machines are exemplified by U.S. Pat. No. 3,762,907, U.S. Pat. No. 3,877,915, U.S. Pat. No. 3,905,793 and U.S. Pat. No. 3,969,703, and U.K. Pat. No. 1,441,099. In all of these prior art patents the basic premise has been to assume that one must have timing means responsive to a drive shaft or the like to provide an instantaneous indication of the elapsed time in each cycle of operation of the machine. In U.S. Pat. No. 3,762,907, U.S. Pat. No. 3,877,915 and U.S. Pat. No. 3,969,703, and in U.K. Pat. No. 1,441,099 a pulse generator provides 360 or more pulses per machine cycle, and is driven by a drive shaft associated with the molten glass feeder, or the take away conveyor, so that the "timing means" for the glassware machine is continually related to the speed of rotation of a rotating machine member. In U.S. Pat. No. 3,905,793 no pulse generator is used, but means is provided for generating a binary coded decimal signal indicative of the instantaneous position of a shaft, and the said signal is compared, sequentially, to a programmed sequence of events stored in memory for producing the necessary output signals to control the machine events.
All of these prior art systems require that a shaft, or other rotating member, be closely monitored during the machine cycle, and that a real time comparison be made to provide the output signals for the various events (usually an "on" or "off" signal to solenoid valves) in the typical Hartford I. S. type glassware forming machine.
In a typical Hartford I. S. type of glassware forming machine, molten glass gobs are delivered from a feeder, by means of a gob distribution system, in a predetermined sequence to the upwardly open blank molds of the various machine sections. Each section comprises a self-contained unit which includes a blank mold station and a blow mold station. The gob of molten glass is formed into a parison at the blank station, and then transferred to the blow station by a neck ring arm which includes a neck mold. The neck mold not only mates with the blank mold at the blank station but also serves to support the parison during transfer to the blow station.
The blank mold may be of the split or the solid type and is adapted to mate with the neck mold. The neck mold is of the split type, and is annular in shape with a central opening to receive a vertically reciprocable plunger which presses the gob into the blank mold in the "press and blow" process, or which plunger is associated with a thimble to permit the parison to be formed by the "blow and blow" process. This latter process provides for "counter blow" air at the blank station in addition to the "final blow" air at the blow station. The description to follow is not limited to either process.
The glass gobs are formed at a rate dictated by the size and shape of the ware to be produced, and these gobs are fed through a distribution system to the various blank mold cavities. Each blank cavity is upwardly open, and a funnel is usually provided to move in onto the closed blank mold for guiding the gob into such cavity. The gob drops through the funnel into the cavity, and into the neck mold, which is always closed except for a short time at the blow station for release of the parison. In this "delivery mode" of the machine the plunger and the thimble must be raised to define the neck opening of the ware. This initial mode is triggered either upon "start up" of the machine, or of a master section thereof, or in accordance with the gob distributor system.
The next mode of operation of the machine can be characterized as one of "settling" the gob or charge into the neck mold. This is accomplished in the usual "blow and blow" process by bringing a baffle down onto the funnel, and providing air to the baffle for "settling" the charge in the blank mold. If no funnel is used in loading the gob, the baffle may move directly in on top of the blank mold. As so configured the blank station of the machine section is in its "parison settle" mode. After settle blowing has been completed the baffle, and funnel, are returned to their inactive positions, respectively.
The next mode of operation of the machine occupies only a short time, and can be characterized as "parison corkage reheat". The plunger moves downwardly away from the neck of the parison allowing the heat of the glass to stablize in this part of the parison. This short pause softens the glass surface by internal conduction, at least in the area where the plunger tip has caused it to cool during the "delivery" and "settle" modes, and as so configured the machine is in its "corkage reheat" mode.
The next mode of operation of the machine can be characterized as one of "parison forming", and in the "blow and blow" process such forming is carried out by introducing counter blow air to the softened area of the parison. The mechanical machine configuration is only altered from the previous mode in that the baffle is lowered onto the blank mold. This mode will see the gob expanded to fill the upper regions of the blank cavity defined by the blank mold and by the baffle. After allowing time for this preliminary forming the counter blow air is turned off, the baffle is returned to its inactive position, and the split blank mold is ready for opening. As so configured the blank station of the machine is in its "parison forming" or "counter blow" mode.
The next mode involves "reheating" parison and the initial phase is accomplished simply by opening the split blank mold. With the blank mold open the parison is not in contact with any mold parts except the neck mold. This configuration allows the heat stored in the thick walled parison to raise the temperature of its external surfaces, hence the derivation of the term "reheat" mode. This phase can be called "blank side reheat".
Once the blank mold has completely opened, the neck ring arm inverts the neck mold and the parison along with it. This phase of the reheat mode can be characterized, thermodynamically, as "invert reheat". This reheating continues at least until the parison has been transferred to the blow station. As the parison reaches the blow station the third phase of reheat occurs. The blow mold closes around the parison and around a bottom plate, which will be spaced below that end of the parison opposite its neck or open end. The blow mold has an upper portion which supports the parison from just below its finish, allowing the neck mold to be opened prior to revert, or return movement of the neck ring mold. The neck ring mold recloses during return movement so that the blank mold can close around it once the neck mold has returned to the blank station.
The next mode involves final forming of the body of the ware, the finish of the ware having been formed by the neck mold at the blank station and during transfer. The final blow air is delivered to the interior of the parison by a blow head which moves down onto the top of the closed blow mold. After a preset time for final blowing the air is turned off and the blow head returned to its inactive position. The blow mold opens and take-out tongs (open) are swung into the blow station. The tongs close around the newly formed ware and the article is lifted off the bottom plate for delivery to the deadplate portion of a take-away conveyor system.
The above described cycle of operation is representative of the typical I. S. machine, and the various events can be seen to comprise simply the turning on or off certain valves in each machine section. This is achieved by the control of solenoids through the control system to be described. The concept of dividing up the cycle into various modes is described in the prior art U.S. Pat. No. 3,877,915 and U.S. Pat. No. 3,905,793. However, these prior art patents, and the others referred to above, do not provide for programming the time period of the machine cycle itself. Insofar as changes to the speed of the feeder, or take away conveyor drive shaft are encountered in these prior art systems, changes to the frequency of a pulse generator tied thereto will necessarily be encountered.